The present invention relates to a method of controlling an internal combustion engine according to the preamble of the independent patent claim.
Such a method is already known from Unexamined German Patent 197 15 774, which describes a method of controlling an internal combustion engine, at least one operating variable, e.g., a firing angle of one or more cylinders or the air supply being controlled by an actuating element. The firing angle and air supply are controlled on the basis of torque values, the firing angle being adjusted according to predetermined firing angle efficiencies. The firing angle efficiencies are taken into account in controlling the idling air in the sense of maintaining engine torque. The firing angle efficiencies are determined as a function of operating parameters of the engine such as the rotational speed and relative cylinder charge. The pre-control ignition timing efficiency is one of such firing angle efficiencies, which ensures that a change in torque is implemented only through the firing angle. If a torque request exceeds a limiting value for a firing angle, the air supply is altered accordingly. More precisely, the pre-control ignition timing efficiency ensures that a worsening of the efficiency setting performed in the firing angle path is taken into account in the air path in such a way that the torque set via the charge changes exactly by the same amount as that set on the basis of the firing angle. The transition between certain operating states is taken into account in the method described in Unexamined German Patent 197 15 774, in such a manner that a predetermined firing angle efficiency is altered in a manner that is not described in greater detail. This predetermined firing angle efficiency is compared with a base firing angle efficiency in a minimum value selection stage, the smaller value in each case, i.e., the inferior efficiency, being output as the pre-control ignition timing efficiency. The base firing angle efficiency describes an efficiency which is obtained from a firing angle of the internal combustion engine at the instantaneous operating point without any external intervention and a firing angle having the highest efficiency under the instantaneous operating conditions, as indicated in Unexamined German Patent 197 15 774.